Tree-Shaking Default Parameters

This demo tests how various bundlers handle Libauth's WebAssembly crypto implementations (ripemd160, sha1, sha256, sha512, and secp256k1).

As a pure ESM library, Libauth v2 can asynchronously instantiate each WASM implementation internally, exporting simple interfaces that behave like collections of JS-only functions (with better performance).

Many of Libauth's exported functions also use one of these built-in WASM instances as a default parameter. For example, decodeBase58Address has the definition:

export const decodeBase58Address = (
  address: string,
  sha256: { hash: (input: Uint8Array) => Uint8Array } = internalSha256
) => {
  // ...
};

Most applications can call decodeBase58Address(address) to automatically use the default, WASM-based sha256 implementation (internalSha256). See src/app-default.js.

Applications that already have another sha256 implementation can provide that implementation as the second parameter: decodeBase58Address(address, mySha256Implementation). In this case, the default parameter (internalSha256) is dead code and should be possible to eliminate from the application's bundle (commonly called tree shaking in the JavaScript ecosystem). See src/app-shakable.js.

Bundler Support

This repo tests dead-code elimination of unused default parameters as used in Libauth (with asynchronously instantiated WASM implementations): src/app-shakable.js.

Currently, dead-code elimination of unused default parameters is only supported by Rollup.

Bundler	Support	Issue	PR
esbuild	❌ (example)	evanw/esbuild#2185	-
parcel	❌ (example)	parcel-bundler/parcel#7961	-
rollup	⏳ (example)	rollup/rollup#4466	rollup/rollup#4498
terser	❌ (example)	terser/terser#1199	-
webpack	❌ (example)	webpack/webpack#15671	-

This simpler example may also be useful for quickly testing support in bundlers:

package.json:

{
  "type": "module"
}

module.js:

// should not appear in bundle:
const internalAdd = (a, b) => (a === '0' ? b : a + b);

export const addAndLog = (a, b, impl = internalAdd) => console.log(impl(a, b));

app.js:

import { addAndLog } from './module.js';

const myAdd = (a, b) => a + b;

addAndLog(1, 2, myAdd); // => 3